The present invention relates to an apparatus for controlling an electric power consumed by an amplifier including a GaAs field effect transistor (FET), and in particular to an apparatus for controlling an electric power consumed by an amplifier including a GaAs FET capable of minimizing a variation in gain, a variation in phase, and a deviation of gain within a band for the amplifier. Description of the Related Art
In a conventional apparatus for controlling an electric power consumed by an amplifier including a GaAs FET, a positive voltage having a fixed value is continuously supplied from a power supply circuit to a drain region of the GaAs FET and a negative voltage having a variable value is delivered from a power supply to a gate region of the GaAs FET. The negative voltage fed to the gate region is controlled according to a value not less than a pinch-off voltage of the GaAs FET to alter a source-to-drain or drain current (ID), thereby controlling the power consumed by the GaAs FET.
However, in the conventional power controller of this type, the drain current is changed by varying the gate voltage of the GaAs FET to control the power consumption, which leads to considerably large changes respectively in the gain, the phase, and the deviation of gain within a band. The changes in the gain and phase cause an alteration in the quantity of improvement of distortion; moreover, the variation in the deviation minimizes a compensation bandwidth of the GaAs FET. This consequently leads to a drawback that in a linear amplifier in which a component of intermodulation distortion appearing in an amplifier including a multi-stage connection is compensated for by cancelling the distortion component with a component having an identical amplitude and an opposite phase with respect to those of the distortion component, the compensation cannot be easily achieved.
In order to improve the disadvantageous feature, there is required quite a fine and complex control in consideration of the gain and phase, which leads to a problem that the hardware configuration and software system are complicated and increased.